YJIT: Fix unread field lint in release builds

```
warning: fields `blue_begin` and `blue_end` are never read
```

yjit/src/disasm.rs

@@ -7,6 +7,7 @@ use crate::options::DumpDisasm;
 
 use std::fmt::Write;
 
+#[cfg_attr(not(feature = "disasm"), allow(dead_code))]
 #[derive(Copy, Clone, Debug)]
 pub struct TerminalColor {
     pub blue_begin: &'static str,

yjit/src/options.rs

@@ -152,7 +152,6 @@ pub enum DumpDisasm {
     // Dump to stdout
     Stdout,
     // Dump to "yjit_{pid}.log" file under the specified directory
-    #[cfg_attr(not(feature = "disasm"), allow(dead_code))]
     File(std::os::unix::io::RawFd),
 }